Summary

Mononeuropathies of the lower extremities are commonly encountered in clinical practice. A mononeuropathy may result from pathology located anywhere along the course of the peripheral nerve, from the dorsal root ganglion through to the lumbosacral plexus and the terminal individual named nerves. Dysfunction can lead to weakness, pain, or sensory deficits. These entities are a major source of neurological referral.

Causes

Mononeuropathies can be thought of as compressive or idiopathic, or as sequelae of underlying systemic disease (e.g., diabetes, malignancy, infection, and inflammatory conditions). Compressive neuropathies produce symptoms in the distribution of the affected nerve root, plexus, or individual nerve. Viral infections such as herpes zoster virus, herpes simplex virus (HSV), Epstein-Barr virus (EBV), and cytomegalovirus (CMV) can involve nerve roots, leading to a painful radiculitis, or may trigger a Guillain-Barre syndrome 1 to 3 weeks after infection. This is more commonly seen in people with altered immune function: for example, older people or those with HIV. Vasculitic neuropathy usually occurs suddenly and is painful. The typical vasculitic picture is stepwise involvement of multiple individual nerves (mononeuritis multiplex) rather than an isolated mononeuropathy.
[1]Preston DC, Shapiro BE. Electromyography and neuromuscular disorders: clinical-electrophysiologic correlations. Boston, MA: Butterworth-Heinemann; 1998.[2]Gorson KC. Vasculitic neuropathies: an update. Neurologist. 2007;13:12-19.
http://www.ncbi.nlm.nih.gov/pubmed/17215723?tool=bestpractice.com
Because individual nerves are affected, one does not see the distal and symmetrical (e.g., stocking-glove) distribution of deficits typical of a generalised polyneuropathy, at least early on. In advanced cases, however, a confluent pattern can emerge that mimics that of a length-dependent polyneuropathy. Mononeuritis multiplex may also be seen with infection. Cancer can produce nerve dysfunction secondary to compression by solid tumours, infiltration by malignant cells, or paraneoplastic immune-mediated attack.

Lumbosacral plexopathies

Neuropathy involving the lumbosacral plexus. It can be caused by compressive, infectious, malignant, and inflammatory aetiologies.

Lumbosacral radiculopathies

Neuropathy involving the nerve root. It can also be caused by compressive, infectious, malignant, and inflammatory aetiologies.